The present invention relates generally to liquid measurement, and more particularly to a method and apparatus for ascertaining the depth of cryogenic liquid in a container.
Cryogenic temperatures are necessary for such processes as the long-term storage of biological materials and the generation of superconductivity. Cryogenic temperatures are sustained through the use of cryogenic liquids, such as liquid nitrogen, that have very low boiling temperatures. Such cryogenic liquids are typically circulated from a storage container to provide cryogenic cooling for a desired application. Accordingly, it is important to be able to accurately gauge the amount of cryogenic liquid remaining in a storage container.
The cryogenic nature of the cryogenic liquid, that very property which makes the cryogenic liquid valuable, also makes the measurement of the amount of cryogenic liquid in a container difficult. The extremely low temperatures of the cryogenic liquids are hostile to measurement techniques that involve mechanical measurements transmitted through motion linkages. This is in part due to the different mechanical and physical properties exhibited by sensor materials when exposed to cryogenic temperatures, such as extreme thermal expansion differentials, excessive brittleness, increased stiffness, and the like. Likewise, while some electronic techniques are better suited for cryogenic liquid measurement, electronic measurement techniques tend to either require bulky and/or expensive equipment or must be permanently installed in the container.
Therefore, there remains a need for a quick, simple and portable technique for measuring the amount of cryogenic liquid in a container. The present invention addresses this need.
The present invention relates to a method and apparatus for measuring the depth of a cryogenic liquid in a container. The apparatus includes a tube having a proximal opening, a distal opening and a generally cylindrical body extending therebetween defining the border between a tube interior and a tube exterior, a resistance heater positioned within the tube substantially adjacent the distal end, a microcontroller in electrical communication with the resistor, and a pressure sensor connected in pneumatic communication with the proximal opening of the tube. The pressure sensor forms a pneumatic seal with the tube. The microcontroller is adapted to selectively actuate the resistance heater to evaporatively remove liquid from the tube, increasing the gas pressure therein and on the pressure sensor. Fluidic communication between the tube interior and the tube exterior is restricted to the distal opening. The microprocessor receives a voltage signal from the pressure sensor in proportion to the gas pressure in the tube and in turn calculates the depth of liquid displaced from the tube.
One object of the present invention is to provide an improved method and apparatus for measuring the depth of liquid in a container. Related objects and advantages of the present invention will be apparent from the following description.